The ability of a NOX storage catalyst to store oxides of nitrogen decreases with increasing age. The storage capacity decreases above all in a lower temperature range of the NOX storage catalyst. The NOX storage catalyst can be operated in a temperature range of 200 to 500 degrees Celsius, for example. The storage capacity then decreases substantially in the range from 200 to 300 degrees Celsius, for example. In contrast thereto, the storage capacity can decrease only slightly in the range above 300 degrees Celsius during the same period of operation.